At Tuesday’s GOP presidential debate in Las Vegas, Herman Cain came under attack for his 9-9-9 tax plan. On Wednesday, Texas Gov. Rick Perry’s embrace of a flat tax caused a stir. And at a town hall event Thursday in Sioux City, Iowa, Mitt Romney criticized a plan offered by Jon Huntsman.

The Huntsman plan would scrap tax deductions entirely, including those for mortgage interest and charitable donations, in order to offset the costs of lowering rates for individuals and corporations. The plan was modeled on the proposal outlined by President Barack Obama’s deficit-cutting panel.

“Well, if you get rid of that, people who bought homes who are deducting their interest on their mortgages for their taxes are going to find that that’s going to cost them money and was something that was unexpected,” Mr. Romney told the crowd in Sioux City. “And it might not help the home industry, as well. Buying and selling homes right is probably not something we want to hurt.”

Mr. Romney also criticized proposals to replace the income tax with a national sales tax, a proposal that shares some features of Mr. Cain’s now-famous plan for a 9% personal income tax, a 9% corporate income tax and a 9% national sales tax.

“It raises taxes on middle-income families,” he said. “I don’t like the idea of raising taxes on middle-income Americans. I think we ought to be lowering taxes on middle-income Americans. So, for me, that’s a non-starter.”

In walking Iowa voters through his positions on the many tax proposals that have been offered, Mr. Romney even raised some concerns about the idea of a flat-tax that Mr. Perry, one of his top rivals, plans to unveil next week. “The flat tax has some positive features,” Mr. Romney said. “But you have to look and make sure it doesn’t raise taxes on middle-income Americans.”

He explained his focus on middle-income Americans this way: “For me, one of the key criteria in looking at tax policy is to make sure we help the people who need the help most,” Mr. Romney said. “And in our country, the people who need the help the most are not the poor, who have a safety net, and not the rich, who are doing just fine, but the middle-class.”

As for his own tax policies, Mr. Romney wants to lower the corporate tax rate to 25% from 35% and eliminate taxes on interest and dividend income for anyone who makes less than $200,000 a year.

“To do that, without losing revenue, we’ll get rid of some of the special breaks that have been put in the tax code by the various lobbyists, the various industry groups, over the years,” Mr. Romney said. The former Massachusetts governor supports lowering the tax rates on individuals, but hasn’t specified how far he’d like to go.

Former Utah Gov. Huntsman, shot back with a statement this afternoon, saying, “Through his record, his proposal, and his comments today Governor Romney has made it abundantly clear that he opposes meaningful tax reform like the kind we implemented in Utah which took us to number one in the nation in job growth…

“Our campaign has offered bold tax reform that eliminates special interest carve-outs, subsidies, loopholes, deductions, and corporate welfare while lowering rates across the board to create a tax code that is flatter, fairer, simpler and more conducive to growth. While our economic plan has been described as ‘the most pro-growth proposal ever offered by a U.S. presidential candidate,’ Governor Romney only wants to nibble around the edges of a broken system.”

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Washington Wire is one of the oldest standing features in American journalism. Since the Wire launched on Sept. 20, 1940, the Journal has offered readers an informal look at the capital. Now online, the Wire provides a succession of glimpses at what’s happening behind hot stories and warnings of what to watch for in the days ahead. The Wire is led by Reid J. Epstein, with contributions from the rest of the bureau. Washington Wire now also includes Think Tank, our home for outside analysis from policy and political thinkers.